In the present study, attempts were made to identify the potential of bacterial strains for promoting Arachis hypogaea L. growth. Four hundred and thirty three bacteria were isolated from rhizosphere, phyllosphere and plant tissues from peanuts cultivated in the producing area of Cordoba, Argentina. From this collection, 37 epiphytic isolates and 73 endophytic isolates were selected on the basis of tricalcium phosphate solubilizing activity. These isolates were further tested for other plant growth-promoting attributes and some of them evaluated to examine the effect of inoculation on peanut growth. Siderophore production was observed in a high percentage of the isolates, especially in the root nodule endophytes. Antibiosis was evaluated against the phytopathogen fungus Sclerotinia minor and S. Sclerotiorum. Endophytes from nodules showed the highest levels of fungal growth inhibition. A low number of isolates was able to produce auxin like molecules and inoculation of peanut seedlings with these bacteria showed variability on seed germination enhancement. Isolate J49, identified to belong to genus Pantoea, was the most promising bacterium because it increases peanut plant biomass in inoculation experiments. Peanut soils in the province of Cordoba harbor bacteria with major plant growth promotion properties which represent a potential source of new strains that could be used as biological inoculants in agriculture.

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The leguminous crop Arachis hypogaea L. (peanut) is originally from South America and then was disseminated to tropical and subtropical regions. The dissemination of the crop resulted in peanut plants establishing a symbiotic nitrogen-fixing relationship with a wide diversity of indigenous soil bacteria. We present in this review, advances on the molecular basis for the crack-entry infection process involved in the peanut-rhizobia interaction, the diversity of rhizobial and fungal antagonistic bacteria associated with peanut plants, the effect of abiotic and biotic stresses on this interaction and the response of peanut to inoculation.

In this study, attempts were made to analyze mechanisms involved in the bacterial phosphate-solubilizing ability of peanut isolates. Bacteria were taxonomically identified by analysis of 16S rDNA sequence. Levels of soluble P released by the isolates in unbuffered or buffered with Tris-HCl or MES NBRIP-BPB medium as well as the production of Dgluconic acid were determined in their culture. Presence of two of the genes encoding the cofactor PQQ of GDH enzyme was analyzed in the genome of this bacterial collection. 16S rDNA sequence analysis indicated that isolates belong to genera Serratia, Enterobacter, Pantoea, Acinetobacter, Bacillus and Enterococcus. All bacteria showed ability to solubilize tricalcium phosphate either in unbuffered or buffered medium. Nevertheless, addition of buffer solutions reduced levels of Pi liberated by the isolates. Although almost all isolates produced detectable amounts of D-gluconic acid, no correlation with levels of P soluble released were observed. The presence of pqqE and pqqC genes was detected only in Gram negative bacteria. It was concluded from this study that the mechanism involved in phosphate solubilization is organic acids production and, presence of pqq genes in all Gram negative bacteria analyzed encourages to confirm their role in bacterial phosphate solubilizing ability as well to identify genes involved in this PGP trait in Gram positive bacteria.

The aims of this study were, to analyze in vitro phosphate solubilization activity of six native peanut bacteria and to determine the effect of single and mixed inoculation of these bacteria on peanut and maize plants. Ability to produce organic acids and cofactor PQQ, to solubilize FePO and AlPO and phosphatase activity were analyzed. Also, the ability to solubilize phosphate under abiotic stress and in the presence of pesticides of the selected bacteria was determined. The effect of single and mixed bacterial inocula was analyzed on seed germination, maize plant growth and in a crop rotation plant assay with peanut and maize. The six strains produced gluconic acid and five released cofactor PQQ into the medium. All bacteria showed ability to solubilize phosphate from FePO and AlPO and phosphatase activity. The ability of the bacteria to solubilize tricalcium phosphate under abiotic stress and in presence of pesticides indicated encouraging results. Bacterial inoculation on peanut and maize increased seed germination, plant́s growth and P content. Phosphate solubilizing bacteria used in this study showed efficient phosphate mineralizing and solubilization ability and would be potential P-biofertilizers for peanut and maize.